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Title: Ultrafast carrier dynamics in organic-inorganic semiconductor nanostructures
Author: Yong, Chaw Keong
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2012
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This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within the inorganic semiconductors. Inorganic semiconductor nanowires and their blends with semiconducting polymers have been investigated using state-of-the-art ultrafast optical techniques to provide information on the sub-picosecond to nanosecond photoexcitation dynamics in these systems. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising nanowires in hybrid organic photovoltaic devices, revealing the performances to date. The experimental methods used during the thesis are detailed in Chapter 3. Chapter 4 describes the crucial roles of surface passivation on the ultrafast dynamics of exciton formation in gallium arsenide (GaAs) nanowires. By passivating the surface states of nanowires, exciton formation via the bimolecular conversion of electron-hole plasma can observed over few hundred picoseconds, in-contrast to the fast carrier trapping in 10 ps observed in the uncoated nanowires. Chapter 5 presents a novel method to passivate the surface-states of GaAs nanowires using semiconducting polymer. The carrier lifetime in the nanowires can be strongly enhanced when the ionization potential of the overcoated semiconducting polymer is smaller than the work function of the nanowires and the surface native oxide layers of nanowires are removed. Finally, Chapter 6 shows that the carrier cooling in the type-II wurtzite-zincblend InP nanowires is reduced by order-of magnitude during the spatial charge-transfer across the type-II heterojunction. The works decribed in this thesis reveals the crucial role of surface-states and bulk defects on the carrier dynamics of semiconductor nanowires. In-addition, a novel approach to passivate the surface defect states of nanowires using semiconducting polymers was developed.
Supervisor: Herz, Laura Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Advanced materials ; Nanomaterials ; Microscopy ; Laser Spectroscopy ; Photochemistry and reaction dynamics ; Spectroscopy and molecular structure ; Nanostructures ; Materials processing ; Semiconductor devices ; Processing of advanced materials ; Single crystal semiconductors ; Condensed Matter Physics ; ultrafast spectroscopy ; photoluminescence ; Mott transition ; semiconductor nanowires ; exciton ; carrier cooling ; hot-carrier ; type-II heterojunctions ; charge transfer ; carrier dynamics ; lifetime ; doping ; trapping